Treatment chemicals, also termed chemical additives, are introduced into the fluid in the systems, following monitoring or diagnosis of a particular problem or to improve performance. The term may include polymeric scale inhibitors, phosphonate scale inhibitors, corrosion inhibitors, hydrate inhibitors (such as methanol and monoethylene glycol), wax inhibitors, anti-fouling agents, asphaltene inhibitors, hydrogen sulphide scavengers, pH stabilisers, flow additives, anti-foaming agents, ethanol, enhanced oil recovery polymers, detergents and demulsifiers. Such chemicals are commonly used in the oil and gas industry, particularly in oil and gas wells, oil and gas pipelines and petrochemical processing plants and refineries and on the forecourt of gasoline pumping stations.
Methanol is a commonly used additive. Major uses of methanol include use in antifreeze, as a solvent, direct use as fuel, a denaturant for ethanol to prevent “liquor” taxes being applied, synthesis of biodiesel and in feedstock. Methanol is particularly useful in the offshore oil and gas industries. Methanol is the most widely used hydrate inhibitor in crude oil production (hydrates are crystals of water and gas) because it is inexpensive and easy to produce.
Methanol is injected into wells to prevent plugging and freezing of gas pipeline in cold areas, which helps to avoid costly downtime due to freeze-ups of deep water well systems.
Monitoring of methanol is crucial for a number of reasons. For example, it is necessary to monitor methanol exposure in the work place for toxicity reasons. It is important to conduct environmental monitoring, for example of industrial effluents, to prevent unacceptable levels of pollution. Methanol levels must be monitored in fuels and fuel emissions, as well as in food, beverages and consumer products to prevent human exposure. Finally, it is useful to determine levels of methanol in biological samples from normal, poisoned and occupationally exposed individuals.
Within the oil and gas industry, monitoring of methanol is especially important, in order to control methanol levels. Methanol content can have an effect on hydrocarbon permit limits and bioremediation at refinery wastewater facilities. Methanol is miscible with water; in a multiphase oil, water and gas stream, the majority will get carried with the water in the system and may be disposed of to the sea or may be transported to the refinery, although some will partition to the hydrocarbon phase. When the refinery processes crude containing methanol the majority of the methanol is removed with the water and sent to the water treatment system where it can drastically upset the balance of the system leading to EPA permit excursions. This happens because the bacteria used to breakdown other components prefer the methanol instead, leaving other hydrocarbons & toxins untreated. A big enough upset can also lead to a “bug kill” which renders the treatment system useless and typically requires major remediation to get the system back in balance. Refineries will typically opt to cut runs vs. risking a permit excursion and future penalties. Methanol can also drastically lower the efficiency of the activated titanium catalyst used in gas fractionation processes. Methanol that remains in the hydrocarbon phase moves into the profitable propane stream sending it off specification and may result in costly flaring. Typically, terminals, refineries and processing facilities will opt to cut runs rather than risk a permit exclusion and future penalties. They will look to recoup these costs by discounting crudes, applying levies for the use of methanol or charging suppliers if levels go above an agreed limit. This is especially problematic when a number of systems that share the same export pipeline are started up and so use methanol at the same time, a situation that can occur during hurricane season in the Gulf of Mexico, or where multiple suppliers share a common export pipeline.
Monoethylene glycol is another commonly used additive, also known as MEG, ethylene glycol, 1,2-ethanediol or ethane-1,2-diol. Major uses of MEG include use as a coolant in engines and personal computers, as a deicer, in air conditioning systems, in plastic manufacturing particularly of polyesters and to protect groups in organic synthesis. MEG is commonly used in oil and gas facilities as a hydrate inhibitor and as a corrosion inhibitor in a cocktail of other chemicals. MEG can also be used for dehydration of natural gas streams and natural gas liquids, and is the most common and economical means of water removal.
Monitoring of MEG is important in a number of areas. Detection of poisoning with anti-freeze in serum and other bodily fluids can be done by detection of MEG. Contamination of fuel and lubricants (for example, when as little as 50 ppm MEG gets into lubricating oil systems, the mixture can polymerise into a viscous fluid plugging lines and ports and accelerating wear) can be monitored. Environmental monitoring of MEG is useful, for example there are a number of examples of contamination of water sources including rivers and streams and drinking water from run-off and storm drains from airports e.g. Albany, N.Y., Lambert field, St Louis and Anchorage, Ak. and industrial sites. Finally, MEG in glycol recycling operations can be monitored in order to regulate efficiency of recovery and collection systems.
Within the oil and gas industries, there are many situations in which it is useful to monitor MEG. Minimum inhibitory concentration (MIC) of MEG must be maintained in offshore equipment to prevent hydrate formation and corrosion. MEG may damage catalysts, so that the quality of oil being exported to processing plants and refineries is compromised. Therefore, although the MIC must be maintained, the levels must be monitored to ensure that they do not rise too high, both to prevent use of fluids containing too much MEG and to reduce any charges levied on oil and gas industry operators by refineries due to high levels of MEG. It is also useful to be able to check the efficiency of MEG regeneration and reclamation plants.
Market intelligence indicates that MEG is more expensive than methanol (also used as a hydrate inhibitor) but it can be more easily recovered and reinjected therefore reducing operational costs. MEG regeneration and reclamation systems have therefore been built. A MEG regeneration system is strictly used to remove water from the produced water/MEG mixture whereas; a MEG reclamation system will also remove various other impurities e.g. salt. MEG is also likely to become more important in the future as it is expected the number of sub-sea tie backs, which connect new discoveries to existing production facilities, will increase in areas such as Alaska, necessitating the use of more methanol and MEG. Therefore, it is considered by the industry that MEG will become a more important chemical in the future and so better detection methods will be required.
Other glycols are also used in the oil and gas industry and may require monitoring for efficiency and hazard reasons. For example, glycol enhanced water-based muds can improve injection.
Ethanol is a commonly used fuel and fuel additive, indeed this is the largest single use of ethanol. Gasoline blends consisting of a wide range of ethanol concentrations (20-100%) are used, particularly in countries such as Brazil and the United States. It is important to accurately measure the ethanol content of such mixtures. Knowledge of the gasoline:ethanol ratio can allow improvements to be made to the drivability and cold starting characteristics of internal combustion engines. Too much ethanol can damage engines so monitoring levels in fuel is important. Ethanol may also be used as a hydrate inhibitor, including as a component in industrial methylated spirits. Issues may arise if small amounts remain in the hydrocarbon stream during processing, leading to contamination of the butane stream and reduction in value of the product.
Typical methods for measuring gasoline:ethanol ratios have involved measuring intrinsic properties such as the dielectric constant, thermal conductivity, index of refraction, change in the speed of sound through the mixture and microwave absorption. These methods can often require expensive equipment or knowledge on the detailed properties of the gasoline used. Infrared spectroscopy is a possible alternative but the sensitivity of this technique can be an issue (U.S. Pat. No. 5,239,860).
In addition to there being benefits for terminals, refineries and processing facilities to monitor the levels of methanol, MEG and ethanol in hydrocarbon streams there is also a benefit in monitoring for suppliers. It can be useful for suppliers to monitor and record levels in their own product, so as to show they are meeting specifications. This in turn may help minimise restrictions. Understanding how these chemicals partition between the water and hydrocarbon phases, where hydrocarbon phases can refer to a gas phase, can also help optimise production systems as well as ensuring more accurate reporting of amounts being shipped for processing.
Corrosion inhibitors are widely used in many industries including the oil and gas and water industries. Corrosion inhibitor residuals are difficult to detect, with no ‘simple’ test being available, particularly for offshore use. The impact of better monitoring on regulations in the oil and gas industry would be positive as the current ‘usage equals discharge’ policy is unlikely to hold true since residuals are expected to be present in oil. Better monitoring will have consequences for regulations and environmental discharge. Some progress has been made in determining concentration of components e.g. using ESI-MS. However, detection of corrosion inhibitor residuals remains difficult, particularly offshore.
Gas chromatography is by far the most common method of measuring methanol concentration in the oil and gas sector. Methods include the Standard Method, ASTM D7059. The accuracy for results below 5 ppm cannot be quantified, and such tests typically take 45 minutes for one sample. The ANTEK P 1000 is a methanol specific process/on-line analyser developed by PAC (a supplier of testing and analysis equipment, http://www.paclp.com). The P 1000 Methanol Analyser combines process gas chromatography (GC) with flame ionisation detection (FID).
GC methods are also used in the detection of MEG in a number of sectors, and has been described in a number of publications (Emergency medicine for detection of toxic glycols and alcohols, Williams R H, Shah S M, Maggiore J A and Erickson T B (2000); Simultaneous detection and quantitation of diethylene glycol, ethylene glycol, and the toxic alcohols in serum using capillary column gas chromatography. Journal of analytical toxicology. 24, (7) 621-626). The presence of 5-200 ppm MEG in engine oil can be detected using the ASTM method (D4291-04 Standard Test Method for Trace Ethylene Glycol in Used Engine Oil). ASTM D4291 can be adapted for use with oil field fluids. The MEG is extracted into water and a back extraction can also be incorporated to remove residual organic components. The GC apparatus is calibrated with samples containing known amounts of MEG before running real samples. Each sample run takes 12 minutes, plus 12 minutes for water blank. Running standards used for calibration takes 2 h 48 min. Including the water extraction step, this gives a time of 3 h 20 min for running a single sample. Results show that the minimum quantifiable concentration is 0.5 ppm, and reproducibility at 25 ppm is +/−2 ppm (8%). If the samples contain more than 50 ppm MEG then they must be diluted and reanalysed. Residual MEG on the apparatus column can render further readings unusable and water blanks need to be used, which extends the duration of the assay. Such assays are not automated, as they require extraction funnels and sometimes centrifugation. They are therefore very time consuming.
GC methods are also used to monitor ethanol, for example the percentage of ethanol of the fuel ethanol that is blended into gasoline (ASTM D5501).
GC methods are not ideally suited for offshore use, because they require complex procedures requiring lab time, in-depth training of lab staff and sensitive equipment which may not be robust to offshore environment. Alternatively, samples can be shipped to shore for onshore laboratory analysis. This is costly, time-consuming and results can be delayed.
Some colourmetric methods have been used for aqueous samples (J. Agric. Food Chem. 2004, 52, 3749; Anal. Biochem. 1996, 237, 103; Anal. Biochem. 1997, 244, 357) The presence of oil in samples makes analysis significantly more difficult since the oil scatters the optical signal and may interfere with the action of the detection reagents. For instance the reagents or reaction intermediates may be denatured or may be more soluble in the non-aqueous phase and therefore be removed from the aqueous phase.
For the purposes of this patent application, the term ‘fluids immiscible with water’ includes oils, gas, condensate, heavy oil, export oil, hydrocarbon streams, waxes, biofuels, biodiesels, petroleum products, lubricants and products from refining, distillation and processing of oil and gas products and also including those with quantities of water, gas or both.
For the purposes of this patent application, the term ‘first reagent(s) refers to chemicals or enzymes that react or interact with treatment chemical in a sample to generate a first product. This first product may be optically detectable. The term ‘second reagent(s)’ refers to chemicals or enzymes that react with the first product to generate a second product that is optically detectable. Preferably the first or second product is fluorgenic, or chromogenic, although may be luminescent or IR- or raman-active. More specifically, where methanol is to be detected preferably the first reagent oxidises methanol to produce formaldehyde or hydrogen peroxide as the first product, which is detected with the second reagent MBTH, Fluoral-P Amplex Redor Purpald. If the sample contains ethanol and methanol then preferably catalase is added to remove interference from ethanol. Where MEG is to be detected preferably the first reagent lead tetraacetate, periodate or periodic acid is used to oxidise the sample with the second reagents MBTH, Fluoral-P or Purpald used for detection of the formaldehyde produced. If a corrosion inhibitor is to be detected then preferably chromogenic agents that react with aromatic groups, unsaturated bonds, hydroxyls or amine groups are used preferably NanoOrange®, nile red, Laurdan, FM 4-64 and 2,6-ANS. If ethanol is to be detected, preferably the first reagent oxidises ethanol and preferably the first reagent is alcohol dehydrogenase.
For the purposes of this patent application the term reactive includes any reaction or interaction between treatment chemical and reagents which forms a different chemical or results in a detectable change in the sample.
The term ‘extraction’ refers to transferring the treatment chemical from a fluid that is immiscible with water to an aqueous phase. The term ‘separation’ means the physical separation of the two phases into separate vials.